Floating gate cells are typically integrated with high voltage (HV) and low voltage (LV) transistors in semiconductor devices such as NAND flash memories. A single thin oxidation is typically used to build both LV metal oxide semiconductor substrate (MOS) and LV cell structure. In such a case, an LV oxide and a tunnel oxide may grow on the substrate during the same process step. Such a single process step and a resulting structure, however, may limit scalability and reliability of the resulting structure.